The present invention relates to an electrochromic display cell and, more particularly, to a method for making an electrochromic display layer in an electrochromic display cell.
Recently, an electrochromic display cell has been developed, which generally comprises two opposing electrochromic layers formed on electrodes, and a liquid electrolyte disposed therebetween. Tungsten oxide is most commonly used for the electrochromic layer, and its coloration/bleaching reaction is considered as follows: When the coloration current is applied to the electrochromic layer, the tungsten oxide (WO.sub.3) layer changes to a tungsten bronze (M.sub.x WO.sub.3 : where x &lt;1) due to the double injection of the electrons caused by the coloration current and metal positive ions (generally, alkali metals M.sup.+) derived from the liquid electrolyte. This reaction creates lattice defects, and the tungsten W(+5) changes to tungsten W(+6) upon every removal of one M.sup.+ from MWO.sub.3 (x=1).
Accordingly, the coloration/bleaching operation is greatly influenced by the chemical structure of the electrochromic display layer (WO.sub.3 layer). More specifically, the response speed of the coloration/bleaching operation, the coloration efficiency, the operation life period, the display quality, etc. are influenced by the method for making the electrochromic layer.
One conventional method for making the electrochromic layer employs the vacuum evaporation technique or the spattering technique to form the solid oxide film. This method requires a vacuum evaporation apparatus, and the control thereof is very complicated. The chemical structure of the electrochromic layer is influenced by the evaporation condition, for example, the evaporation rate, the pressure, and the substrate temperature. Therefore, this method is not suited for mass production.
Another conventional method for making the electrochromic layer is to paint a gel mixture of powder electrochromic material. This method is not practical since the layer formed through this method does not show a desirable transparency. Accordingly, an object of the present invention is to provide a novel method for making an electrochromic display layer.
Another object of the present invention is to provide an electrochromic display cell which ensures a stable operation.
Still another object of the present invention is to provide a method for making an electrochromic display layer suited for mass production.
Yet another object of the present invention is to provide an electrochromic display layer of stable construction and showing a high electrochromic efficiency.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, an electrochromic display layer is formed in the following manner. A metal compound, for example, tungsten chloride (WCl.sub.6) is dissolved in an organic solvent such as methanol, iso-butanol or ethanol. The thus obtained organic solution is disposed on the electrode carried by the substrate through the use of, for example, a dipping method. Then, the organic solution layer is calcined to form the electrochromic layer having a stable construction.